It was carried out a comprehensive observation and analysis of a mixed convectivestratiform precipitation in Beijing on 30 June, 2007, by using IP/WVP3000 groundbased microwave radiometer, Doppler radar, satellite data, ground gauge and other observational data. The results showed that, there was a marked increase in the total liquid water content detected by the groundbased microwave radiometer, before the start of precipitation. Precipitation lagged behind the emergence of liquid water content began to increase for some time. By use of that phenomenon, it may be early warning in the stage of the development of precipitation, and applied to artificial rainfall. It showed that the vertical distribution trends of radar reflectivity and liquid water content detected by groundbased microwave radiometer had a good relationship, when detecting at the same time and same location. In addition, the distribution of the cloud liquid water, especially the lowlevel liquid water, had a direct relationship with the ground rainfall.